The quality of community-supplied water has come under increased scrutiny. Consumers have become aware of decreasing water quality and have turned to water treatment devices to remove undesirable chemical and/or microbiological components in the water. Domestic and commercial water treatment devices are well known in the art. Typical devices are incorporated into a water system either in-line, at a terminal end, or as a self-contained system which processes water in batches. An example of an in-line system would be an under-the-counter device which filters water prior to reaching the faucet. Terminal end devices include countertop and faucet-mounted filtration units. Self-contained batch devices rely on an influent holding chamber and an effluent holding chamber which are connected through a filtration cartridge.
Typical water treatment devices use mechanical filtration or chemical removal media. Mechanical filters treat water by preventing passage of particulates such as sediments, turbidity, and if fine enough, colloidal matter. As a mechanical filter approaches the end of its useful life, reduced or stopped flow due to particulate accumulation provides a ready indication that element replacement is necessary.
Chemical removal media (e.g. charcoal-based media and ion exchange media) employ processes such as adsorption and ion exchange for removing undesirable chemical species. The problem with chemical removal media is that the removal of undesirable chemicals eventually decreases and stops as the effective life of the chemical removal media ends, and the cartridge does not provide any indication to the user that the chemical removal media therein is no longer effective.
As a result, various approaches have been taken to indicate end of life to the user where it is not inherently provided by the behavior of the media. One example is shown in U.S. Pat. No. 4,686,037 (Lang). In this approach, a pre-filter is used to entrap contaminants, and the color of the pre-filter is compared by the user with a reference strip to determine when the media requires replacement. Drawbacks to this approach, are that color determination involves human judgment, making it subjective and subject to error. Additionally, users may easily forget to check the reference pre-filter and mistakenly believe the spent media is still treating the water passing through the pre-filter.
A more accurate means of indicating end of life of conventional treatment units is through devices which use a process known as "flow totalization." These devices totalize the liquid volume which has passed through the media. Flow totalization-based devices have become recognized as the most accurate means for end of life indication. For example, NSF International, the certifying agency in the United States for water treatment devices, requires for certification of rated volume use of twice the filter media capacity when an end of life indication means is not used, and only 20% additional capacity when an indicator is employed.
Both electrical and mechanical approaches to "flow totalization" are disclosed in the prior art. U.S. Pat. No. 4,918,426 (Butts et al.) and U.S. Pat. No. 5,089,144 (Ozkahyaoglu et al.) disclose the electrical approach. The devices disclosed in these patents use pressure transducers with outputs which are integrated to calculate total volume. After a predetermined volume has been reached, a valve is electrically actuated to stop flow.
Examples of mechanical devices are disclosed in U.S. Pat. No. 4,681,677 (Kuh et al.) and U.S. Pat. No. 4,698,164 (Ellis). These devices typically include a turbine interconnected with a series of gears which mechanically "add up" the volume of water passed through the device. The gears are interconnected with a valve such that, after a predetermined volume of water has passed through the device, the valve is mechanically actuated to stop flow.
Although flow totalization addresses the end of life problem, there are drawbacks. One drawback is that flow totalization devices are expensive and complex, as they must be designed to exacting specifications. An additional drawback with mechanical flow totalization devices is that the automatic indicator mechanisms, are generally too bulky to be included in a compact device. Moreover, they are not practical for a batch device which operates at low flow rates and low pressures.
In that regard, the consumer batch filtration field includes devices such as carafe units, for example, U.S. Pat. No. 4,895,648 (Hankammer), and a Mr. Coffee.RTM., Model No. WF 1. The Hankammer ('648) patent discloses a device including an annular surface of a disk with markings indicative of the months of a calendar year and an adjustable pointer. After the filter is installed in this device, the pointer is set to the month that the device was installed.
A drawback to this device is that its life expectancy is based on an estimate, and it does not actually determine when the effective life of the cartridge is over. Furthermore, even if the pointer was set on the appropriate month during which the filter cartridge is to be replaced, the manufacturer presumes a set number of uses per time period for the purpose of calculating useful life. As a result, varied usage is not accounted for.
The Mr. Coffee.RTM. carafe includes a mechanical ratchet mechanism connected to an indicator dial and the water outlet of the carafe. Upon use, the user manually actuates the ratchet mechanism once for each pitcher of treated water desired. As a result, the estimated lifetime of the filtration media is more accurately tied to the volume of the water actually treated. When filtration of a batch of water is desired, a window connected to a stiff spring is slid open, which simultaneously increments the ratchet mechanism and shuts the exit port. The ratchet mechanism is connected to the visual indicator dial. After filling the carafe, the window is shut, which opens the exit port. Once the indicator dial reaches the end of life position, a key is used to reset the rachet/spring mechanism.
This device exhibits drawbacks in that its use is inconvenient as the window must be actuated in each direction when a carafe of purified water is desired. Additionally, the key is crucial to proper operation, and if lost, the device is rendered useless. Moreover, this device is bulky and requires a large number of intricate and expensive components.